Field of the Invention
The present disclosure relates to the field of air compressors adapted for use on rail vehicles for supplying compressed air to pneumatic units associated with the rail vehicle and, in particular, to an oil-free air compressor on a rail vehicle for supplying compressed air to various pneumatic units associated with the rail vehicle.
Description of Related Art
The use of a multiple stage, multiple cylinder air compressor is well known in the art. It is common practice to use a multiple stage, multiple cylinder air compressor on a locomotive or other rail vehicle to provide compressed air that is consumed by various pneumatic devices throughout the locomotive and railcars to provide a variety of critical functions. One of these primary functions is to operate the locomotive and railcar brakes. The traditional oil-flooded reciprocating compressors utilized commonly throughout North America are three cylinder, two stage compressors that are available in many different models and configurations. One of the most common configurations for a compressor is a compressor with two first stage or low pressure cylinders and one second stage or high pressure cylinder. This compressor is often configured in a “W” configuration with the low pressure cylinders banked at 60 degrees to each side of the vertical high pressure cylinder. The compressor utilizes a large oil sump to provide lubrication and internal component cooling.
A less common and more recent approach to a locomotive air compressor is to use oil-free reciprocating compressors in place of the traditional oil flooded variety. This oil-free technology reduces the need for a large oil sump in the compressor housing and allows for different cylinder configurations to achieve specific improvements such as torque pulse control, dynamic balancing, and overall size reductions. A problem commonly associated with the new oil-free reciprocating compressors is overheating, which can lead to the compressor shutting down or operating at an inefficient level. Some current oil-free reciprocating compressors also experience high torque pulses and uneven dynamic balancing and are designed to improve one of these features at the expense of the other or at the expense of a larger overall compressor size. An example of an oil-free air compressor for a rail vehicle is disclosed in U.S. patent application Ser. No. 14/030,588 to Kapadia et al., filed on Sep. 18, 2013, incorporated herein in its entirety.
By nature of its design, a reciprocating compressor transfers rotary motion of a crankshaft to reciprocating motion of one or more pistons through a matched number of connecting rods. A reciprocating air compressor uses a connecting rod to connect the rotating crankshaft (at a crank pin) to reciprocating pistons (at a wrist pin). The connections between the wrist pin, piston, connecting rod, and crankshaft must include a bearing surface capable of handling the oscillating or rotating motion and the associated loads from inertial, frictional, and gas compression forces. There are many acceptable bearing types and mounting methods used to create a reliable bearing and component assembly. The connecting rods contain bearings to transfer load and motion from the compressor crankshaft through the connecting rod to the wrist pin and piston assembly.
In a traditional oil-flooded air compressor, the bearings may be of a variety of the types such as plain bearings, ball bearings, rollers bearings, etc., as the oil provides necessary cooling and lubrication. This variety allows the use of split bearings which aid in the assembly of the air compressor. In an oil-free air compressor, a variety of bearings may also be utilized. There are advantages, however, to using single piece bearings as opposed to split bearings, especially in regards to the life of the air compressor and the design simplicity. At the same time, these advantages are offset by disadvantages of such designs of the connecting rods that affect the size of the air compressor, complexity to assemble the air compressor, maintainability, and the life of the air compressor.
There is a current need for an oil-free reciprocating compressor with a reduced overall size and a reduction in torque pulse. There is also a current need for an oil-free reciprocating compressor with improved dynamic balancing and improved air flow for cooling the cylinders of the compressor. There is also a current need for improved compressor housing ventilation. There is also a current need for a single piece bearing assembly on a crankshaft end of a connecting rod that can reduce the size of the connecting rod, improve the interchangeability of the connecting rods, improve the field of maintainability of the air compressor, and simplify installation of the connecting rod.